package hg;

import java.util.Scanner;

public class M0104 {
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		double epsilon = 0.0001;
		while (in.hasNext()) {
			double x = in.nextDouble();
			if (x < 0) {
				System.out.println(Double.NaN);
				continue;
			}
			for (double bc = 0;; bc += epsilon) {
				if ((x - (bc * bc)) < epsilon || (bc * bc) >= x) {
					System.out.printf("%.6f%n", bc);
					break;
				}

			}
			in.close();
		}
	}
}
